This invention relates to charging flowable materials into selected cells of a honeycomb structure and, more particularly, to a method and apparatus for selectively manifolding, i.e., plugging, cells of a honeycomb structure for the fabrication of ceramic filter bodies and other selectively sealed honeycomb structures, such as particulate traps for diesel engines.
Honeycomb structures having traverse cross-sectional cellular densities of approximately one tenth to one hundred cells or more per square centimeter have several uses, including solid particulate filter bodies and stationary heat exchangers. Such uses require selected cells of the structure to be sealed or plugged by manifolding and the like at one or both of the respective ends thereof. The term “sealed” and other corresponding grammatical forms, i.e., sealant, sealing, etc., are used herein to refer to both porous and non-porous methods of closing the open transverse cross-sectional areas of cells.
The reference numeral 10 (FIG. 1) generally designates a solid particulate filter body that is generally well known and that may be fabricated utilizing a honeycomb structure 12 formed by a matrix of intersecting, thin, porous walls 14 surrounded by an outer wall 15, which in the illustrated example is provided a circular cross-sectional configuration. The walls 14 extend across and between a first end face 18 and an opposing second end face 20, and form a large number of adjoining hollow passages or cells 22 which also extend between and are open at the end faces 18, 20 of the filter body 10. To form the filter 10 (FIGS. 2 and 3), one end of each of the cells 22 is sealed, a first subset 24 of the cells 22 being sealed at the second end face 20, and a second subset 26 of the cells 22 being sealed at the first end face 18 of the filter 10. Either of the end faces 18, 20 may be used as the inlet face of the resulting filter 10.
In operation, contaminated fluid is brought under pressure to an inlet face and enters the filter 10 via those cells which have an open end at the inlet face. Because these cells are sealed at the opposite end face, i.e., the outlet face of the body, the contaminated fluid is forced through the thin porous walls 14 into adjoining cells which are sealed at the inlet face and open at the outlet face. The solid particulate contaminant in the fluid, which is too large to pass through the porous openings in the walls, is left behind and a cleansed fluid exits the filter 10 through the outlet cells and is ready for use.
For the mass production of such filters and heat exchangers, it is highly desirable to be able to seal selected cells ends as rapidly and as inexpensively as possible. A well-known method of fabricating filter bodies is to manifold or plug the end of each cell individually with a hand held, single nozzle, air actuated gun. The hand held plugging of individual cells by this process is long and tedious and is not well suited for the commercial production of such filters, heat exchangers, and other honeycomb structures which have thousands of cells to be selectively sealed.
Another known method of plugging includes the use of a mask having a number of openings extending therethrough for selectively manifolding honeycomb structures in the fabrication of solid particulate filter bodies. These masks typically include a rigid plate having a number of bores extending therethrough.
Masks have also been formed for manifolding cells which are regularly interspaced among substantially mutually parallel rows and substantially mutually parallel columns at an open face of a honeycomb structure by applying strips of an adhesive backed flexible webbing impermeable to the sealed material, such as masking tape, over selected rows and columns of cells. Alternatively, these masks are created by providing a matrix of spaced, overlaid strips of resilient, impermeable and reusable material such as metal foil, which are then joined together and fitted, with or without an underlying gasket, over the open surface of the structure with the openings through the matrix and gasket positioned opposite the cells to be charged. By providing a honeycomb structure with cells arranged in mutually parallel rows and mutually parallel columns and covering alternative rows and alternate columns of cells with strips of a suitable flexible material such as the masking tape or the joined thin metal strips, the open ends of one-half of a subset of cells arranged in a checkered pattern across the open face are exposed. After filling the ends of these strips, the strips are removed and strips are applied covering the remaining alternate rows and remaining alternate columns, thereby exposing the open ends of the remaining half of the subset of cells of the checkered pattern at the end face for filling. Both embodiments provide greater flexibility in dealing with the surface height variations and provide better masking of the cell ends not to be charged, including those which may be damaged, than does the rigid plate embodiment. However, both embodiments must typically be applied twice to each end face. This is a significant limitation with respect to the tape strips which must be individually applied across each end face, a time consuming task. The reusable matrix and gasket of the second embodiment may be more quickly applied and removed, but like the rigid plate embodiments, is less easily adapted to distortions in the cell locations at the end faces. Moreover, increasing cellular densities render such an approach unworkable.
In another approach, the rigid plate is provided with a plurality of bores extending therethrough to register with the open ends of alternate cells of a honeycomb structure. Each bore is fitted with a short filling tube which protrudes from the face of the plate and into a cell when the plate is aligned over the open cell ends of the honeycomb structure. A sealing material is forced from the opposing face of the plate through the bores and into the cell ends receiving the tubes. However, this approach is inflexible, a limitation which becomes increasingly significant when cell densities in the honeycomb structure are increased and distortions in the locations of the cell walls become relatively more severe. The rigid construction of this approach also damages brittle honeycomb structures.
In yet another approach, rigid rivets are attached at regular intervals along the length of thin flexible strips and run along alternate diagonals of cells arranged in mutually parallel rows and mutually parallel columns, wherein each rivet is inverted into and covers the open end of the cell along the diagonal. As a result, half of the cells exposed at an end surface of the honeycomb structure are covered in a checkered or checkerboard pattern and the open ends of the remaining cells are filled in a single sequence of steps. The strip-backed rivets are more flexible but require more handling than either of the plate embodiments discussed above, thereby lessening their appeal for use in selectively large honeycomb structures on a commercial basis.
In still yet another approach, plates containing a plurality of spaced apart spherically-shaped bearings are pressed against the ends of the filter. The bearings are spaced at intervals so as to engage alternate cells. The shape of the bearings causes the walls of the alternate cells to collapse inwardly towards one another, thereby sealing the ends of the cells not occupied by the bearings. However, significant forces are required to “crush” the walls sufficiently, the application of which may cause unintentional deformation of the filter, such as shearing of the ends of the walls. Further, a suctioning force generated between the bearings and the filter makes the bearing-containing plate difficult to disengage from the filter, and again may result in unintentional deformation of the filter.
A method for manifolding or plugging extruded honeycomb structures, such as ceramic particulate traps for diesel engines, is desired that is highly repeatable and accurate, while simultaneously having a short cycle time. The method should also be easily applied, be adapted to non-uniform cell patterns, and reduce unintended deformations of the desired structure.